Closed circuit process for the production of expanded polystyrene foam

Abstract

A closed circuit process for the production of expanded polystyrene foam is described, comprising the steps of: (a) pre-expanding raw polystyrene beads containing a blowing agent in a pre-expansion vessel; (b) storing the beads in one or more closed storage containers to allow the expanded beads to return to substantially atmospheric pressure; (c) molding the expanded beads to a desired configuration in a closed mold with steam; and (d) removing the thus-formed article from the mold and placing such in an aging room, wherein at each stage the blowing agent released from the beads is recovered, separated from any residual steam by means of a condensing system, and introduced into the burner of a steam generator, thereby serving as fuel for the process.

What is claimed is: 
     
       1. A closed circuit process for the production of expanded polystyrene foam comprising the steps of: (a) pre-expanding raw polystyrene beads containing a blowing agent in a closed pre-expansion vessel;   (b) storing said beads in one or more closed storage bins;   (c) molding said expanded beads to a desired configuration in a closed mold with steam; and   (d) removing the thus-formed article from the mold and placing such in an aging room, wherein during each of said steps the blowing agent released from the beads is recovered, avoiding release of the blowing agent into the surrounding atmosphere, and     (e) separating the recovered blowing agent from any residual steam by means of a condensing system.   
     
     
       2. The closed circuit process as claimed in claim 1, wherein said blowing agent is selected from the group consisting of n-pentane, iso-pentane, butane, hexane and mixtures thereof. 
     
     
       3. The closed circuit process as claimed in claim 2, wherein said blowing agent is n-pentane. 
     
     
       4. The closed circuit process as claimed in claim 1, wherein steam produced by a steam generator is introduced into said pre-expansion vessel. 
     
     
       5. The closed circuit process as claimed in claim 1, wherein said pre-expansion vessel is a pressurized pre-expansion vessel which operates at a pressure of from about 6 psi to about 15 psi and a temperature of about 212° F. to about 230° F. 
     
     
       6. The closed circuit process as claimed in claim 1, wherein a residual mixture of steam, air and blowing agent released during pre-expansion is transported from said pre-expansion vessel in an exhaust pipe through a condensing system wherein the blowing agent is separated from steam and recovered. 
     
     
       7. The closed circuit process as claimed in claim 6, wherein said condensing system comprises a scrubber and/or a condensing tank. 
     
     
       8. The closed circuit process as claimed in claim 1, wherein a residual mixture of steam, air and blowing agent released during molding is transported from said mold in an exhaust pipe through a condensing system wherein the blowing agent is separated from steam and recovered. 
     
     
       9. The closed circuit process as claimed in claim 8, wherein said condensing system comprises a scrubber and/or a condensing tank. 
     
     
       10. The closed circuit process as claimed in claim 1, wherein said closed storage bins operate at approximately atmospheric pressure. 
     
     
       11. The closed circuit process as claimed in claim 1, wherein the mixture of air and blowing agent released from the beads during storage is vented from said closed storage bins through an outlet and is transported through a duct to an inlet of the burner of a steam generator or an afterburner. 
     
     
       12. The closed circuit process as claimed in claim 1, wherein said pre-expanded beads are transported from said pre-expander vessel to said closed storage bins and from the closed storage bins to the mold by means of closed pneumatic conveying systems. 
     
     
       13. The closed circuit process as claimed in claim 12, wherein the air used to transport the pre-expanded beads in said pneumatic conveying systems is recirculated within a closed duct system avoiding any release of the blowing agent into the surrounding atmosphere. 
     
     
       14. The closed circuit process as claimed in claim 7, wherein the condensing tank is approximately half-filled with water which is kept at a temperature between about 104°-140° F. 
     
     
       15. The closed circuit process as claimed in claim 9, wherein the condensing tank is approximately half-filled with water which is kept at a temperature between about 104°-140° F. 
     
     
       16. The closed circuit process as claimed in claim 1, wherein the aging room operates at negative pressure and a temperature between about 100° F. and about 140° F. 
     
     
       17. The closed circuit process as claimed in claim 1, wherein the closed mold operates without releasing air, steam, pentane or mixtures thereof into the surrounding atmosphere. 
     
     
       18. The closed circuit process as claimed in claim 6, wherein the blowing agent recovered is transported through a duct to an inlet of the burner of a steam generator or an afterburner. 
     
     
       19. The closed circuit process as claimed in claim 8, wherein the blowing agent recovered is transported through a duct to an inlet of the burner of a steam generator or an afterburner. 
     
     
       20. The closed circuit process as claimed in claim 1, wherein said aging room enhances the release of the remaining blowing agent content of the molded articles stored therein, and also avoids release of said blowing agent into the surrounding atmosphere. 
     
     
       21. In a process for the production of expanded polystyrene foam comprising the steps of: (a) pre-expanding raw polystyrene beads containing a blowing agent in a closed pre-expansion vessel;   (b) storing said beads in one or more closed storage bins;   (c) molding said expanded beads to a desired configuration in a closed mold with steam; and   (d) removing the thus-formed article from the mold and placing such in an aging room, the improvement which comprises performing said process in a closed system by recovering said blowing agent during each of said steps, avoiding release of said blowing agent into the surrounding atmosphere, and separating the recovered blowing agent from any residual steam by means of a condensing system.